Process of metallizing electrotype-molds.



- HYMAN ELI GOLDBERG, OF CHICAGO, ILLINOIS.

PROCESS METALLIZING ELECTROTYPE-MOLDS.

No Drawing,

Specification of Letters Patent. Application filed August 2, 1911.Serial No. 642,082.

Patented Sept. 3, 1912.

To all whom it may aoncem:

Be it known f that I, HYMAN ELI GOLD- BERG, a citizen of the UnitedStates, residing at Chicago, in the county of Cook and State ofIllinois, have invented a certain'new and useful Process ofMetallizingElectrotype- Molds, of which the following is a specificati n,

My invention relates to 'the process of metallizing or preparingelectrotype molds to make them conductive in order of the application offine flake graphite in dry state to said mold. This process is veryobjectionable because the graphite fiies about in all directions to thegreat inconvenience of the workmen. This has been overcome by theconstruction of special machines which brush the graphite onto the mold,but it nevertheless remains a lengthy and delicate operation. Anothermethod consists in the application of metallic powder, for instance,bronze, to the mold and then applying a solution like silver nitrate orsome other metallic salt in order to cause it to take. This process isnot used much in practice on account of its inconveniences. There areother processes, namely, the treatment with silver nitrate andphosphorous, and the treatment'with silver nitrate and sulfuretedhydrogen. These methods are inconvenient and laborious and requireconsiderable time, and frequently unless the work is very carefully donethe results are imperfect and unsatisfactory.

The object of my invention is to simplify, cheapen and improve theso-called process of metallizing and is accomplished in the followingmanner I first prepare a solution of a conductive solid in colloidalform in a volatile liquid, then apply this solution to the nonconductive mold and finally dry the mold, thereby evaporating thesolvent and causing the conductive substance to be deposited on the nonconductive mold. Among the properties of colloidal metals is the onethat upon evaporation of their solvent they become non colloidalorinsoluble. In process the metal is, therefore, deposited uponthe moldin a coherent, continuous, insoluble, electrically,

conductive layer. Among the conducting solids which I employ for thepreparation of the colloidal solution maybe-gold, silver, or graphite,et cetera, but I prefer copper. Among the solvents for the solids arewater, alcohol, ether, glycerin, acetone, etcetera.

One method of obtaining cop er and other metals in colloidal form is toorm a direct current arc under waterbetween terminals consisting of themetal to be rendered colloidal. Other methods are explained by Theo.Svedberg in his published book upon the subject, entitled H erstellungKolloz'der Loesungen Anorgam'scher Stojfe, 1909 edition, published byTheodore Steinkopff, Dresden, Germany. He describes methods applicableto organic solvents such as alcohol, ether, glycerin and acetone and themethod consists in forming an alternating current are in the liquidandintroducing the metal, for example, silver or copper, in finelydivided form, for example, small pieces of foil or thin sheets. Thevarious processes are listed in the index at the end of the book, forinstance, those relating. to copper are'listed on page 506.

It is the common practice to employ wax asthe substance for making theelectrotype mold. It will be found generally that a water colloidalsolution will not wet wax readily. This objection may be avoided bytreating the mold previously to the application of the colloidalsolution, with alcohol or similar liquid. I greatly prefer, however,

to avoid the necessity for this alcohol pretreatment by employing as thesolvent one which has a greater attraction for wax than water, and assuch solvent I- prefer ether. Another advantage in employing other as asolvent is that whereas a colloidal solution of copper in water spoilsvery readily by the oxidation of the copper such oxidation occurs veryslowly in ether. Copper, of course, is an excellent conductor, andfurthermore, copper is the metal usually employed in electrotyping andconsequently by employing copper for the metallizing substance I -avoidmixing metals. Therefore, for all of these reasons I greatly prefer onthe whole to use a colloidal solution of copper dissolved in ether.

' Of course electrotype molds areordinarily prepared from wax, but it iswell known that galvano plastic molds are made from other substancesalso, for instance, gutta percha, plaster of Paris, et cetera. Theliquid that I use for a solvent depends upon the composition of themold. For a mold of gutta ercha I employ benzol as a solvent, for I findthat a solution prepared from this as'la solvent readily'wets a guttapercha m0 d.

I find that in practice in using ether as a solvent'the operator has tobe ve rapid in his work on account of the rapidity of evaporation of theether. Moreover, the ether if too thickly applied makes the wax rathersoft. For both of these reasons I sometimes use. a mixture of ether andalcohol instead of ether alone.

In practicing my method I sometimes pour the colloidal solution onto themold and thus form a layer upon it or again sometimes apply it with abrush or sometimes di the mold completely in the coll'oidal so ution.

Having thus described my invention,

what v I claim as new, and desire to secur by Letters Patent, is:

1. The herein described process of producing an electrically conductivelayer upon ting the said solvent to evaporate.

. 2. The herein described process of producmg an electrically conductivelayer upon a surface, such as a mold, which consists in first applyingto the mold surface a colloidal solution of a metal in-a volatilesolventand then permitting the said solvent to evaporate.

In witness whereof, I have hereunto subscribed my name in the presenceof two witnessesl HOWARD M. Cox, MARGARET D. R033.

